Summary: Opal: A Single Address Space System
for 64­bit Architectures
Jeff Chase, Hank Levy, Miche Baker­Harvey, Ed Lazowska
Department of Computer Science and Engineering
University of Washington
Seattle, WA 98195
Abstract
The recent appearance of architectures with flat 64­bit virtual addressing opens an opportunity to
reconsider the way our operating systems use virtual address spaces. We are building an operating system
called Opal for these wide­address architectures. The key feature of Opal is a single global virtual address
space that extends to data on long­term storage and across the network. In this paper we outline the
case for the use of a single virtual address space, present the model of addressing and protection used in
Opal, and discuss some of the problems and opportunities raised by our approach.
1 Introduction
The Opal project is an investigation into the effect of wide­address architectures on the structure of operating
systems and applications. Our premise is that the next generation of workstations and servers will use
processors with 64­bit data paths, and sparse, flat, 64­bit virtual addressing. The MIPS R4000 [MIP 91] and
Digital's Alpha family [Dobberpuhl et al. 92] are recent examples of the trend to wider addresses. Our goal
is to determine how software can best exploit the large virtual address spaces of these emerging architectures.
We view the move to 64­bit addressing as a qualitative shift that is far more significant than the move to